In the treatment of patients suffering respiratory ailments, such as emphysema where the patient's lung capacity is severely restricted, it is common practice to provide the patient with a source of oxygen. Typically, this source of oxygen is provided from a pressurized oxygen cylinder which may be located remotely from the patient in a hospital and supplied through suitable tubing (central storage type) or may be an individual cylinder located at the patient's bedside. Since many of these ailments are chronic and require extended therapy, portable oxygen cylinders which the patient may use at home have been developed.
While the use of individual cylinders provides the necessary life-sustaining therapy for these patients, the cylinders themselves present several problems when used in the home. Specifically, since the cylinders contain high pressure (2000 p.s.i.) oxygen, they present a constant danger of fire and explosion during use. The individual cylinders have limited capacity, and therefore must be serviced and replaced routinely thereby increasing the cost of therapy. In addition, there may also be leakage problems which may unexpectedly diminish the capacity of a cylinder so that the patient is left with inadequate therapy gas.
Atmospheric air, which contains about 21% oxygen and 78% nitrogen, provides a vast and abundant source of oxygen. However, until recently technology for extracting oxygen economically for individual use has been lacking. Now, however, membranes have been developed which are adapted to feasible separation of gases.
As is well known to those skilled in the art, separation of gases in membrane technology is based on the selective permeability of certain materials. The term "selective permeability" means that one gas in a mixture will permeate through a membrane faster than a second gas, but this is not to suggest that one gas passes through the membrane to the complete exclusion of all others. Rather, a difference in a flow rate of two molecular species through a permeable membrane results so that the gas mixture on one side of the membrane is depleted in concentration of the more permeable component and the gas on the opposite side of the membrane is enriched with the more permeable component.